Placements.by_id was keyed by the raw 32-bit UID, so an M2 (MDDF) and a WMO (MODF) carrying
the same numeric UID merged: the second registration only bumped the first one's refcount and
never spawned its model (approach-order dependent; e.g. UID 54418 farm.wmo vs redridgefallentree01,
54705 humantwostory.wmo vs elwynnbush09, 55333 redridgedocks02.wmo vs elwynnbush09).
Key is now u64: M2 = uid, WMO = (1<<32)|uid, carried through tile refs, refcount/release, WMO
readiness, straddler bookkeeping, prop merge and collider weld. Spawn metadata keeps the 32-bit UID.
Regression: monkey_mddf_and_modf_with_the_same_uid_stream_independently.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
(cherry picked from commit a55cfa184377f87734a352c6b399adc8833b25eb)
pkuzic
10abf2f4db